Effect of heat stress on serotonin-2A receptor-mediated intracellular calcium mobilization in rat C6 glioma cells

This study was conducted to investigate an effect of heat stress at 44 °C for 30min on intracellular Ca ²⁺ signaling system and on heat shock protein (HSP)-70 expression. 5-HT-induced Ca ²⁺ mobilization was reduced 1, 3 and 6hrs after heat stress, and recovered to the control level 12 and 24hrs after heat stress. One hr after heat stress, Ca ²⁺ rise was significantly decreased when the cells were stimulated by any concentration of 5-HT. Thrombin-induced Ca ²⁺ increase was also markedly reduced 1hr after heat stress. HSP-70 level was increased 6 and 9 hr after heat stress. In HSP synthesis inhibitor quercetin-treated cells, HSP-70 expression was not enhanced after heat stress, and Ca ²⁺ rise in response to 5-HT did not return to the control level. However, the Ca ²⁺ rise induced by 5-HT was not restored to the control level after stress in Ac-Asp-Glu-Val-Asp-H (DEVD)-exposed cells while DEVD had little effect on heat stress-induced synthesis of HSP-70. Dexamethasone did not alter the change in HSP-70 expression or Ca ²⁺ response after heat stress. These results indicate that heat stress attenuated 5-HT-induced Ca ²⁺ mobilization and that HSP-70 expression played an important role in recovery from Ca ²⁺ impairment, possibly via protease activity in C6 cells.